Lecture 6 DNA Replication III Flashcards
Define DNA ligase and its role
An enzyme that synthesizes phosphodiester bonds between nucleotides and is responsible for repair, recombination of DNA strands in replication.
What is FEN1
Flap endonuclease involved in replication of the lagging strand in eukaryotes.
What is the role of Telomerase
It is an enzyme that maintains the ends of linear eukarytoic chromosomes by synthesizing telomeric repeat sequences.
What would happen if Telomerase was not present
The ends of chromosomes will become progressively shorter unless extended by the telomerase enzyme.
Explain what is meant by the lagging strand
The strand of the double helix that is replicated/copied in a discontinuous fashion, in discretes sections known as okazaki fragments.
Explain how the lagging strand is replicated in bacteria.
DNA polymerase III makes the okazaki fragment and stops when it reaches the RNA primer.
DNA Pol I continues the synthesis over primer.
DNA ligase links the two fragments together.
How are Okazaki fragments joined together in E.Coli
DNA Pol I synthesizes over the primer.
DNA ligase joins the two fragments together, forming a phosphodiester bond.
How are Okazaki fragments joined together in Eukaryotes
DNA pol delta and helicase push out the primer.
FEN 1 cuts at the branch point.
There is now a missing phosphodiester link.
DNA ligase seals the strands.
Explain the problem that occurs in replication of linear chromosomes
The final okazaki fragment cannot be made because its priming site woud be beyond the end of the template DNA strand.
Therefore, telomerase is required to extend the template strand, with a series of telomeric repeat sequences.
Telomerase is found in all cells. True or False
False! Telomerase is only found in stem cells
In which cells can telomerase be found
Only in stem cells.
